1. Field of the Invention
This invention relates to an image forming apparatus for recording high-quality graduated images. More particularly, the invention relates to a technique of dividing an input picture into a plurality of blocks and converting its gradation with the size of the blocks so specified that desired screen angles can be achieved in a correct and easy way.
2. Description of the Related Art
Known in the art of multi-color imagery is a method in which data that represents the gradation levels for each of the colors the image is to be recorded in and which are input to an image forming apparatus is divided into blocks each consisting of predetermined regions and the gradation levels of individual pixels are converted within each block on the basis of a transformation matrix having tone conversion characteristics set in correspondence with the position in the block so as to accomplish graduated recording.
If the same transformation matrix is applied to all of the colors in which the image is to be recorded, image deterioration occurs as exemplified by moirxc3xa8s due to interference between recording colors or the clogging up of colors that are placed in the same position. To avoid these problems, multi-color images are recorded using transformation matrices that have different screen angles for the respective recording colors.
However, the transformation matrices having different angles for different colors are not necessarily square in shape and it is often required to set matrices of complex shapes. With a square matrix, blocks into which the data for image""s gradation levels are to be divided need be simply tiled; on the other hand, the transformation matrices having different screen angles for different colors have to be set as those of special shapes so that they have a two-dimensional periodicity and can form the desired screen angles. This setting process requires not only high skill but also a great number of steps to be performed.
The present invention has been accomplished under these circumstances and has as an object providing an image forming apparatus that enables the formation of high-quality multi-level images by ensuring that the size of blocks into which the image is to be divided is specified in accordance with the resolution of the image to be recorded.
The stated object of the invention can be attained by the image forming apparatus, which divides input image gradation level data into a plurality of blocks and which performs graduated recording by converting said divided image gradation level data into multi-level recording data in accordance with gradation conversion characteristics determined as keyed to relative positions in each of said blocks, characterized in that said blocks are set to a size satisfying the following relation:
(55/n) less than X/p less than (65/n), provided p is an integral multiple of 10;
where X is the resolution of the image to be recorded in a given direction and expressed in dpi, p is the length of each block in said given direction and expressed in dots, and n is a natural number.
In this image forming apparatus, the image gradation level data divided into a plurality of blocks is converted to multi-level recording data in accordance with gradation conversion characteristics keyed to relative positions in each block so as to perform graduated recording, with the blocks being set to a size satisfying the relation of (55/n) less than X/p less than (65/n), provided p is an integral multiple of 10. As a result, blocks that provide a screen angle of about 15 or 75 degrees at any resolution of the image to be recorded can be tiled seamlessly in an ordered pattern throughout the image so as to form a high-quality multi-level image with less visible graininess without deterioration in the resolution of the multi-color image.
The stated object of the invention can be also also attained by the image forming apparatus, which divides input image gradation level data into a plurality of blocks and which performs graduated recording by converting said divided image gradation level data into multi-level recording data in accordance with gradation conversion characteristics determined as keyed to relative positions in each of said blocks, characterized in that said blocks are set to a size satisfying the following relation:
(110/n) less than X/p less than (130/n), provided p is an integral multiple of 5;
where X is the resolution of the image to be recorded in a given direction and expressed in dpi, p is the length of each block in said given direction and expressed in dots, and n is a natural number.
In this image forming apparatus, the image gradation level data divided into a plurality of blocks is converted to multi-level recording data in accordance with gradation conversion characteristics keyed to relative positions in each block so as to perform graduated recording, with the blocks being set to a size satisfying the relation of (110/n) less than X/p less than (130/n), provided p is an integral multiple of 5. As a result, blocks that provide a screen angle of about 45 degrees at any resolution of the image to be recorded can be tiled seamlessly in an ordered pattern throughout the image so as to form a high-quality multi-level image with less visible graininess without deterioration in the resolution of the multi-color image.
The stated object of the invention can be also attained by the image forming apparatus, which divides input image gradation level data into a plurality of blocks and which performs graduated recording by converting said divided image gradation level data into multi-level recording data in accordance with gradation conversion characteristics determined as keyed to relative positions in each of said blocks, characterized in that said blocks are set to a size satisfying the following relations:
(36/n) less than X1/p1 less than (44/n)
and
(72/n) less than X2/p2 less than (88/n), provided p1 and p2 are each an integral multiple of 15;
where X1 is the resolution of the image to be recorded in a given direction and expressed in dpi, p1 is the length of each block in said given direction and expressed in dots, X2 is the resolution of the image to be recorded in a direction generally perpendicular to said given direction and expressed in dpi, p2 is the length of each block in said perpendicular direction and expressed in dots, and n is a natural number.
In this image forming apparatus, the image gradation level data divided into a plurality of blocks is converted to multi-level recording data in accordance with gradation conversion characteristics keyed to relative positions in each block so as to perform graduated recording, with the blocks being set to a size satisfying both the relation of (36/n) less than X1/p1 less than (44/n) for a given direction and the relation of (72/n) less than X2/p2 less than (88/n) for a direction generally perpendicular to said given direction, provided p1 and p2 are each an integral multiple of 15. As a result, blocks that provide a screen angle of about 30 degrees at any resolution of the image to be recorded can be tiled seamlessly in an ordered pattern throughout the image so as to form a high-quality multi-level image with less visible graininess without deterioration in the resolution of the multi-color image.
The stated object of the invention can be also attained by the image forming apparatus, which divides input image gradation level data into a plurality of blocks and which performs graduated recording by converting said divided image gradation level data into multi-level recording data in accordance with gradation conversion characteristics determined as keyed to relative positions in each of said blocks, characterized in that said blocks are set to a size satisfying the following relations:
(77/n) less than X1/p1 less than (94/n)
and
(154/n) less than X2/p2 less than (189/n), provided p1 and p2 are each an integral multiple of 7;
where X1 is the resolution of the image to be recorded in a given direction and expressed in dpi, p1 is the length of each block in said given direction and expressed in dots, X2 is the resolution of the image to be recorded in a direction generally perpendicular to said given direction and expressed in dpi, p2 is the length of each block in said perpendicular direction and expressed in dots, and n is a natural number.
In this image forming apparatus, the image gradation level data divided into a plurality of blocks is converted to multi-level recording data in accordance with gradation conversion characteristics keyed to relative positions in each block so as to perform graduated recording, with the blocks being set to a size satisfying both the relation of (77/n) less than X1/p1 less than (94/n) for a given direction and the relation of (154/n) less than X2/p2 less than (189/n) for a direction generally perpendicular to said given direction, provided p1 and p2 are each an integral multiple of 7. As a result, blocks that provide a screen angle of about zero degrees at any resolution of the image to be recorded can be tiled seamlessly in an ordered pattern throughout the image so as to form a high-quality multi-level image with less visible graininess without deterioration in the resolution of the multi-color image.
The image forming apparatus in this invention may be modified such that the blocks correspond to the respective colors in which a multi-color image is to be recorded.
In this image forming apparatus, the blocks are adapted to correspond to the respective colors such as K, C, M and Y in which a multi-color image is to be recorded. As a result, the screen angle can be set to a desired value for each color as selected from among about 15, 30, 45 and 75 degrees, thereby forming a high-quality multi-color image while preventing the clogging up of colors.
The image forming apparatus in this invention may be also modified such that the blocks correspond to the respective colors in which a multi-color image is to be recorded.
In this image forming apparatus, the blocks are adapted to correspond to the respective colors such as K, C, M and Y in which a multi-color image is to be recorded. As a result, the screen angle can be set to a desired value for each color as selected from among about 0, 15, 45 and 75 degrees, thereby forming a high-quality multi-color image while preventing the clogging up of colors.
The image forming apparatus in this invention may be modified such that the blocks are dedicated to recording in cyan and magenta, the blocks to recording in black, and the blocks to recording in yellow.
In this image forming apparatus, the screen angle of the blocks for recording in cyan and magenta is set to either about 15 degrees or about 75 degrees, that of the blocks for recording in black is set to about 45 degrees, and that of the blocks for recording in yellow is set to about 30 degrees, eventually contributing to the formation of a high-quality multi-color image.
The image forming apparatus according toxe2x80x94one of embodiments of this invention may be modified such that a recording head for performing said graduated recording is a thermal head.
In this image forming apparatus, the use of a thermal head as the recording head allows the gradation converted data to be output as energy to be applied to the thermal head so that said data can provide a high-quality graduated record.
The image forming apparatus according toxe2x80x94one of embodiments of this invention may be modified such that it uses a heat-sensitive transfer recording material that has a substantially clear heat-sensitive ink layer in a thickness of from 0.2 xcexcm to 1.0 xcexcm and containing 30-70 parts by weight of a pigment and 25-60 parts by weight of an amorphous organic high-molecular weight polymer having a softening point of 40xc2x0 C.-150xc2x0 C., at least 70% of the pigment in said heat-sensitive ink layer having a particle size of no more than 1.0 xcexcm, and the transfer image having an optical reflection density of at least 1.0 on a white base.
Having the constituent materials of the heat-sensitive transfer recording material specified as above, the image forming apparatus according to claim 12 can produce graduated records of very high quality that are very much like printed matter in terms of color reproduction and texture.